Focusing of an intense neutralized proton beam

An intense low-energy (15–20 keV) proton beam is focused in two stages: ballistic focusing is followed by magnetic compression. The beam is formed by an MAIS wide-aperture source, in which a plasma is generated by many discharge elements via a discharge over the polyethylene surface. In the presence of an external magnetic field, the beam turns out to be overneutralized by electrons coming from the cathode grids of the source and from the target. The maximal focusing efficiency (>70%) is observed within 10 µs after the pulse has been applied if the target is negatively biased. The degree of beam compression in terms of cross-sectional area is 1.6×103. The numerical simulation of the focusing agrees well with the results of measurement.